Vitamin D deficiency: symptoms, levels and what to do (UK)

This entry is part of the Nutri Tailor Health Reference Library — cited research on supplements, nutrients and adjacent areas of health.

Summary

Vitamin D deficiency is defined in the UK by a blood level of 25-hydroxyvitamin D below 25 nmol/L; 25 to 50 is insufficient; 50 or above is sufficient for most people. The symptoms are vague and easy to attribute elsewhere: tiredness, low mood, aching bones and muscles, frequent infections and, in children, soft or bowed bones. Between October and March the UK sun is too weak to make any, which is why UK guidance is that everyone considers 10 micrograms (400 IU) a day over winter. A result below 25 belongs with a GP, who may prescribe a loading course; 25 to 50 is where a daily supplement and a retest at twelve weeks is the usual path.

How it works

Vitamin D is made in the skin from sunlight and stored in fat, then converted by the liver to 25-hydroxyvitamin D, the form the blood test measures, and by the kidneys to the active hormone that governs calcium absorption. Between October and March the UK sun sits too low for the skin to make any, so stores built over summer run down through winter, which is why levels are lowest in spring and why the symptoms are vague: tiredness, low mood, aching bones and muscles and more frequent infections.

Associated supplementsAll supplements in the Nutri Tailor store are GMP-certified, practitioner-grade & made in the UK

Vitamin D3 and K2 Capsules →£33.02This capsule provides vitamin D3 with vitamin K2 as menaquinone 7. Each capsule provides 62.5 mcg of vitamin D3, which is 2500 IU and 200 mcg of vitamin K2. Vitamin D supports the immune system, muscle function and the absorption of calcium and vitamin K contributes to normal bones and normal blood clotting.
Vegan Vitamin D3 and K2 Capsules →£41.52This capsule provides vitamin D3 from algae, the plant source, with vitamin K2 as menaquinone 7. Each capsule provides 62.5 mcg of vitamin D3, which is 2500 IU and 200 mcg of vitamin K2, in a vegetable capsule.
Vitamin D3 Oil Drops →£22.56This is vitamin D3, cholecalciferol, dissolved in avocado oil. Four drops provide 12.5 mcg of vitamin D3, which is 500 IU. Vitamin D supports the immune system, muscle function and the absorption of calcium. It contributes to normal bones and teeth.

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Special populations

Darker skin, covered skin, indoor lives, people over 65, pregnancy and breastfeeding, and anyone with a gut condition that affects fat absorption are the groups most likely to run low. Units matter: UK labs report nmol/L, while home kits and US sources often use ng/mL; multiply ng/mL by 2.5 to get nmol/L, so a result of 30 is deficient in nmol/L and comfortably sufficient in ng/mL.

Guideline positions

Below 25 nmol/L is deficient, 25 to 50 insufficient, and 50 or above sufficient for most people, per SACN and NICE. The bands and their history are set out in what is a normal vitamin D level, and the action level in what vitamin D level needs supplementation.

Practical framework

Read the number with the free blood test result interpreter, and check the action level in what vitamin D level needs supplementation. Choose a form with which form of vitamin D should you buy, and take it with a meal containing fat. Retest at twelve weeks, because the level takes that long to settle, as how long does vitamin D take to work explains. The NHS upper limit is 4000 IU a day without clinical input.

Browse the full range: vitamin D supplements.

Sources

NHS UK. Vitamin D. NHS UK (UK government).
Scientific Advisory Committee on Nutrition (UK government) 2016. SACN Vitamin D and Health report. Scientific Advisory Committee on Nutrition (SACN, UK government).
NICE Public Health Guideline PH56. Vitamin D: supplement use in specific population groups. National Institute for Health and Care Excellence (NICE).
Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, Murad MH, Weaver CM 2011. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology and Metabolism. PMID: 21646368 · DOI: 10.1210/jc.2011-0385
Demay MB, Pittas AG, Bikle DD, Diab DL, Kiely ME, Lazaretti-Castro M, Lips P, Mitchell DM, Murad MH, Powers S, Rao SD, Scragg R, Tayek JA, Valent AM, Walsh JME, McCartney CR 2024. Vitamin D for the prevention of disease: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology and Metabolism. PMID: 38828931 · DOI: 10.1210/clinem/dgae290
NHS Derbyshire Medicines Management; Coventry & Warwickshire Formulary; Nottingham APC; South West London ICB; Shropshire Telford and Wrekin ICB (representative regional NHS formularies). Vitamin D deficiency — primary care management. NHS Derbyshire Medicines Management; Coventry & Warwickshire Formulary; Nottingham APC; South West London ICB; Shropshire Telford and Wrekin ICB (representative regional NHS formularies).
NIH Office of Dietary Supplements. Vitamin D Fact Sheet for Health Professionals. NIH Office of Dietary Supplements (US government).

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